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Old 15th Mar 2021, 10:23 am   #13
snowman_al
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Location: Llandeilo, West Wales, UK.
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Default Re: Leak 20 Project

Quote:
Originally Posted by Westo091946 View Post
...I have the underside wiring of the component pcb if you could call it that, have good photographs and can see the connections to pcb and valve bases, but my problem is under pcb wiring loom I think that this is predominately the valve heater circuit wiring split into two ? with the 6.5-0-6.5 volt split ? between the two channels given the mix of valves and seeing the configuration on the valve bases the ECC83 heaters are pins 4 &5 Linked and 9, 6.3 Volt if pins4,5,6 are connected this would need 12.6V heater voltage, El84 are 4 & 5. 6.3 V and so I am assuming that there are two runs for the valve heaters, and are parallel with centre tap to earth ? also the wiring of the input and output of the output transformers as well. I know that the GZ34 has it own 5 volt supply
...
We were always told, and it's in the Mullard book of amps to twist the heater wires together as this would have a cancelling effect on any emission's from the heater wiring affecting the high gain audio circuitry...
OK
Let's clear up the ECC83 connections and 6.3 volt heater wiring conundrum.
The ECC83 can be used at 12.6 volt if you use pins 4 and 5. (The filaments are then in series and pin 9 is not used.)
It can also be used on 6.3 volts if you link pins 4 and 5 together, for one connection, and then use pin 9 for the other connection. The 2 filaments are now in parallel. (Have a look at the valve data http://www.r-type.org/pdfs/ecc83.pdf.)
Leak use the Parallel method so pins 4 and 5 are linked and pin 9 is used. That way only 6.3 volts is needed.
Also on the Leak the 6.3 volt heater supply is referenced to ground / 0 volts by a centre tap on the transformer, that is one of the hum reduction parts. The heater winding is effectively 3.15-0-3.15 volts.

I've drawn the heater layout in the diagram enclosed, you can match it to the picture. Solid lines are Green wires, dotted lines are Grey wires.

Follow this method and hum (from the wiring) is not a problem.

Quote:
Originally Posted by Westo091946 View Post
... I can get off the self mains transformer but it's the 300-300 which is the very original which they switched for a 280-280 volts the higher HT value is limiting value of the EL84, from my research mullard confirmed to Leak that this was OK (so I read) but leak anyway changed to the lower HT and changed R12 and R13 from 1Meg (300-300)V to R13 and R13 to 470K (280-280)V I do not know the the mA rating for the Mains Transformer so if some one could help here please...
The 300-0-300 will be fine, later build ones have a 300-0-300 volts transformer from the factory. The late build charcoal one in the picture does.
The ratings were mentioned in post #3.

Alan
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Last edited by snowman_al; 15th Mar 2021 at 10:43 am.
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